smooth 0-10v output

The only problem with that circuit might be stability - adding a 47pF capacitor between the opamp output and its inverting (-) input would cure that.

The issue is that the opamp feedback path has to go through a potentially slow component (transistor) and drive a capacitive load (C3) - this might introduce enough phase-lag to induce oscillations. The small capacitor would provide a high-frequency lagless feedback path to quell such a tendancy without affecting low frequency behaviour.